1. Field of the Invention
The present invention relates generally to flat panel displays, and more particularly to an electroluminescent display and method which integrates a driver panel with a processed display panel to form an active-matrix electroluminescent display.
2. Description of the Related Art
Conventional electroluminescent displays use a passive-matrix or edge driven addressing scheme to energize a phosphor panel within the display. A typical passive-matrix electroluminescent display is described in S. Sherr, Electronic Displays .sctn.5.3.2 (2d ed. 1993). The phosphor panel is typically sandwiched between parallel row electrodes on one side of the phosphor panel and orthogonally placed parallel colur electrodes on the other side of the phosphor panel. A display element area is defined at each intersection of the row and column electrodes. A particular display element is activated by the concurrent application of voltage signals to the appropriate row and column electrodes.
Passive-matrix displays present a multitude of problems such as high power losses, slow data rates, and poor control of grey scale uniformity across the display elements of the matrix. The phosphor in electroluminescent displays typically requires a high voltage potential of between 160 and 210 volts for luminescence. This high voltage requirement, coupled with the fact that the row and column electrodes themselves define the display element areas, forces the electrodes to be relatively large in size. The large electrodes create highly resistive paths which leads to large power losses when addressing multiple display elements.
In addition to high power losses, the high resistance of the column and row electrodes results in poor control of grey scale uniformity across the display elements of the matrix. As discussed, each display element is driven by a shared row electrode and a shared column electrode. Consequently, as a particular voltage signal travels through each row and each column, the voltage signal level decreases in proportion to the resistance along the respective electrode path. As a result, a high voltage signal must be used to control grey scale modulation. In addition, the voltage signal applied to each display element varies significantly from one display element to voltage applied to each display element is critical, especially in high resolution displays with a large number of display elements.
Finally, passive-matrix displays generally suffer from slow operating speeds. The slow speed is caused in part by the large electrode size which must be used to address each display element. Further losses in speed are due to the activation of a given row only once per frame. Images on passive-matrix displays usually flicker at the frame rate because the display elements are on for only a fraction of the frame time. This can be unacceptable in high resolution video applications.
Active-matrix addressing differs from the passive-matrix structure described above by incorporating an active device, such as a switching transistor, at each display element. The active device reduces power losses by separating the electrode addressing circuitry from the actual electrodes, thus allowing the use of a smaller grey scale control voltage. Additionally, data rates are increased by a charge storage capability at each active device for providing longer "on time" for each display element. Finally, greater grey scale uniformity is provided by independent control of the voltage signal at each display element. An active-matrix display is discussed in greater detail in S. Morozumi, "Active-Matrix Displays," 2 Society For Information Display 10.1 (1989).
The incorporation of an active drive device at each display element represents a substantial increase in the complexity of electroluminescent displays. The need for a large number of interconnections between the active devices and the display panel makes the manufacture of external driver circuit architectures impractical.